1. Introduction AI display control instruments are widely installed in equipment and systems and used in combination with other instruments in system engineering control projects. This article will analyze and introduce the advantages, methods, and applications of the integrated application of display control instruments and PLCs. In the design of field control systems, it is necessary to consider not only which control equipment to use, but also the purpose of use, the field operation process, the simplicity of construction wiring and panel wiring, and the compatibility of equipment connections: how many units can be connected? What is the connection distance? How to process data? What is the communication speed? Furthermore, the convenience of maintenance, development and design time, and cost are all factors considered in the project. 2. Advantages of Reading Temperature Data to PLC 2.1 Scheme Analysis Adding communication functions to the display control instrument further enhances its added value. By sending measurement data to a computer, touchscreen, or PLC through communication, temperature data can be managed and analyzed, which is beneficial for high-quality production management. To achieve complex mechanical movements, the use of PLCs in equipment is becoming increasingly common. With the continuous development and evolution of control technology, the functions of PLCs are now approaching those of computers. PLCs can not only process data such as bytes, but also communicate with external instruments. Temperature modules using the PLC's PID calculation function require programming, which is complex, tedious, and time-consuming, and also requires programmers with expertise in PID control. If the PLC fails, the temperature control section stops working. By delegating the PID control to an external display and control instrument, with the PLC only providing logic control signals, the external display and control instrument can fully utilize its multiple functions, enabling many functions that the PLC cannot perform. Because the display and control instrument is independent, even if a PLC failure causes the equipment to stop operating, PID display and control can continue. The most significant breakthrough in recent HMI touchscreen development lies in its use of a high-performance RISC CPU, 32MB of large-capacity memory, and CF flash memory card storage that can be expanded from 1 to 4GB. This provides massive data recording capabilities, enabling data and alarm recording functions, recording a complete industrial site data in the CF flash memory card for easy retrieval and saving. 2.2 Advantages of the Solution The advantages of using display and control instruments in conjunction with a PLC are summarized as follows. (1) Significantly reduces the burden on the PLC; (2) Enables functions that the PLC cannot achieve using the unique functions of the display control instrument; (3) Achieves risk dispersion in control; (4) Simultaneously displays sequential status and control data display status on the touch screen or computer; (5) Controls equipment operation based on operating conditions; (6) Displays alarms and communication with equipment in a historical manner; (7) Easily changes parameter settings for each product; (8) Enables programmable temperature control settings; (9) Enables the expansion of CF flash memory card storage function on the computer or touch screen to record data for high-quality production management. 3 Integration Method of Temperature Controller and PLC As mentioned above, the advantages of using display control instruments and PLCs together have been well received by designers and field technicians and have been widely applied. Because the data of the display control instrument was initially managed mainly by computer, the first consideration when developing the communication protocol of the display control instrument was the connection with the computer. The communication protocols between various display control instrument and PLC manufacturers are independent and there is no unified specification. In order to connect the temperature controller and PLC, the communication interface and protocol of the two need to be consistent. 3.1 Method of Programming the Protocol of the External Instrument with Arbitrary Addresses Most PLCs can be programmed according to the protocol of external instruments to communicate with them. Therefore, by writing a communication program on the PLC side that can transmit and receive data in a way that the external instrument can understand, communication can be achieved. This method is quite common. 3.2 Practical Applications In industrial applications, one PLC controller is used to connect multiple display and control instruments to control temperature, liquid level, flow rate, etc., flexibly controlling multiple instruments to achieve the designed control objectives. The programmable controller uses RS-485 communication instructions to easily achieve serial communication with multiple Xiamen [Yu Dian] AI instruments. This successfully realizes flexible control of multiple instruments with a single controller. The programmable controller allows up to 101 [Yu Dian] instruments to be connected to one RS-485 communication interface. When there are more than 60 instruments, an RS-485 repeater is required. The communication distance of the RS-485 communication port can reach over 1.2KM. The serial communication protocol for YuDian AI instruments is RS-485 (1 start bit, 1 or 2 stop bits, 8 data bits, no parity). The baud rate for data transmission is 1.2K, 2.4K, 4.8K, 9.6K, or 19.2K, which can be set in the instrument parameter baud. Figure 1 shows the overall system design block diagram, highlighting the RS-485 interface between the programmable controller and the AI ​​instruments. In industrial settings, RS-485 communication is a widely used communication method. In the diagram, the programmable controller connects to multiple AI instruments via the RS-485 communication interface, up to a maximum of 101 instruments. Each instrument is assigned its own address code for identification (the address code can be set in the instrument parameter Addr). Thus, the programmable controller's RS-485 communication port can control all the connected instruments via the communication cable. [IMG=System Overall Design Diagram]/uploadpic/THESIS/2007/12/2007120611111295632W.jpg[/IMG] This example uses a programmable logic controller (PLC) and AI instruments for RS-485 communication, enabling a single controller to control multiple AI instruments and monitor the operating status of each instrument in real time. The entire system is flexible and convenient to control, with a simple structure, low development cost, and short cycle, and can work stably even in harsh industrial environments. Example: Cold Storage Control: Temperature Controller Communication, Temperature Monitoring and Recording, Timed Defrosting. As more and more manufacturers in the refrigeration and freezing industry face overseas customers, these customers require the recording and reporting of process parameters, mainly temperature parameters, during the refrigeration and freezing process. Therefore, it is necessary to upgrade the existing control system. To minimize investment, adding an RS485 communication module and a domestically produced programmable logic controller (Haiwell PLC) to the existing temperature controller can economically and conveniently meet these requirements. This article will introduce the application of this system. As shown in the diagram above, the system mainly consists of temperature controllers with RS485 interfaces, programmable logic controllers (PLCs), and touchscreens. Working principle: Utilizing the user-friendly communication functions of the Haiwell PLC, the system communicates with 16 temperature controllers via the Haiwell PLC's RS485 port to collect the temperature of each cold storage unit. Then, it communicates with a computer via the Haiwell PLC's RS232 port. Application software on the touchscreen records and collects these temperatures. A. System advantages: 1. The system utilizes Haiwell PLC's dedicated communication instructions MODR and MODW to achieve data reading and setting communication with the AI ​​display and control instrument. All communication functions of the Haiwell PLC can be implemented with a single instruction, eliminating the need for programming special bits or registers, and eliminating the need to manage the communication timing of multiple communication instructions. Multiple communication instructions can be written simultaneously under the same conditions. 2. The Haiwell PLC has a built-in standard Modbus protocol, enabling easy communication with KingSCADA software; 3. Adding a communication module to existing display and control instruments significantly reduces customer investment costs and the amount of work and time required for retrofitting; 4. The Haiwell PLC comes standard with one RS232 port and one RS485 port, and either communication port can be used as a master or slave station. Either communication port can also be used as a programming port or a port for communication with third-party devices. In this application, the RS232 port is used for communication with the computer, and the RS485 port is used for communication with the AI ​​Yudian display and control instrument. B. Main Hardware Configuration: 1. Programmable Controller: HW-S32ZS220R 1 unit 2. AI Display and Control Instruments (AIBUS): 16 units 3. Touch Screen: 1 unit C. Program Design Highlights: 1. Communication with AI display and control instruments is easily achieved using MODR and MODW instructions; 2. Daily timed defrosting function is achieved with a single instruction using the built-in real-time clock function and TIME instruction of the Haiwell PLC; Utilizing the convenient communication function and instruction set of the programmable controller (Haiwell PLC), the acquisition and recording of process parameters in the refrigeration and freezing process is realized economically and efficiently, meeting the international requirements of customers. It can be widely used in the renovation of old systems and the technical upgrade of new systems in the refrigeration and freezing industry. 3.3 Open Fieldbus Method Open fieldbus, also called open network, is a specification published by various PLC manufacturers. Because the various instruments connected to the PLC are standardized to the same specification, instruments from any manufacturer can be connected. Manufacturer differences do not need to be considered when developing the program. These open fieldbuses have various specifications developed by different PLC manufacturers, resulting in a sense of fragmentation. AI instruments correspond to various fieldbuses, as mentioned above. 4. Conclusion Display and control instruments control temperature, pressure, and flow, while PLCs control sequential actions, allowing each to leverage its strengths. Their data is managed through communication, improving productivity. This demonstrates the powerful advantages of display and control instruments in control systems, leading to their widespread application.